[asterisk-users] asterisk, iaxmodem, hylafax quality problem

[Lee Howard]

Artifex Maximus wrote:

> Everything is fine when caller use ECM but when ECM isn't in use I
> often got unusable incoming faxes (much often that it should be). But
> when I switch back to fax machine that receive faxes perfectly (at
> least no visible error).


The fax machine itself uses ECM, undoubtedly.  If callers that have 
quality problems with IAXmodem+HylaFAX don't have problems with the fax 
machine, then that strongly indicates that something is wrong with your 
Asterisk setup... corrupting the audio.  Usually this is due to resource 
constriction of the Zap device, zttest scores less than 99.98% is 
indicative of that situation.

> Where should be the problem? Is there any solution for improving
> quality? Any tuning in Asterisk or Hylafax? As I see some people use
> slinear for iaxmodem and some user use alaw. Which is better? 


There is no functional difference between using uLaw, alaw, or 
slinear... except that using slinear reduces the need for conversion... 
and thus possibly lessens CPU usage very slightly.

Lee.